The present invention relates generally to transfer mechanisms for advancing workpieces through a plurality of work stations in an automated machining line and relates to U.S. Pat. No. 3,798,981, assigned to the assignee of the present application. U.S. Pat. No. 3,798,981 discloses a drive mechanism which imparts cyclical reciprocal movement to a single transfer bar. When the transfer bar engages and advances a plurality of workpieces, all workpieces are moved through the same distance corresponding to the length of the stroke of the transfer bar. Consequently, all adjacent work stations must be spaced apart equally a distance equivalent to the length of the stroke of the transfer bar, in order to advance each workpiece the entire distance from one work station to the next work station.
Sometimes it is necessary to set up the machining line with some adjacent work stations spaced apart distances greater than the length of the stroke of the transfer bar. As a result more than a single stroke is required to advance the workpieces between those work stations resulting in the use of idle stations at which these workpieces are temporarily stored. Some workpieces, therefore, are not machined while other workpieces at their respective stations are machined. The workpieces are carried on pallets or advanced in a free transfer system in which no pallets or other workpiece supports are used.
When pallets are used, additional ones are needed to ensure that all work stations are occupied for a machining operation after each advancing stroke. Pallets and idle stations are costly in known transfer systems.
It is the general object of this invention, therefore, to provide a drive mechanism in a transfer apparatus operable to contemporaneously move a plurality of workpieces through unequally spaced work stations leaving no workpiece stranded between work stations.